The advantages and disadvantages of being small, long, and skinny illustrated in Figure 2.8 tend to cancel each other out. There are no one-for-one tradeoffs but, in general, weasels have both a substantial advantage over other, larger predators in hunting efficiency and the disadvantage of being vulnerable to attack by them. Weasels have the advantage of being able to increase production rapidly in good years but the disadvantage of risking starvation in bad years. Most important, the metabolic penalties incurred by a small animal in a cold climate are all serious. The size and shape of a weasel are hugely inefficient in physiological terms, and impose real energetic costs to living the weasel way of life.
To supply the massive energy they need, weasels have huge appetites. Captive animals eat between a quarter and a third of their body weights each day, and more active wild ones probably eat more (Table 2.1). They are tied to a life of frequent small meals, five to ten a day, and to the necessity of finding food at frequent intervals (Gillingham 1984). None of them, especially not least weasels, can endure going without food for long, which is one of the difficulties of live-trapping them. Nearly all this enormous intake of food is burnt up merely to keep warm.
The alert, rapid movements of weasels reflect their constant hunger, geared-up metabolism, and galloping pulse—measured at rest at about 360 to 390 beats per minute in stoats and 400 to 500 beats per minute in common weasels (Tumanov & Levin 1974; Segal 1975). If you put your ear to the chest of an anesthetized weasel, you can hear the heart "purr-r-r-ring" away, but you cannot count the heartbeats. This frantic pace of life is also reflected in the anatomy of organs that have to do with metabolic processes. The load on the heart and lungs is great, so the heart is large relative to the weight of the body, especially in small individuals. A weasel's food comes in large, infrequent packages, so the digestive system is adapted to deal with alternate feast and famine. The gut is short and meals pass through quickly. Dyed bait fed to a least weasel reappears in 2 to 4 hours, and the defecation rate is high, averaging 19 scats per 24 hours (Short 1961). Weasels often nap after a meal, but not for long.
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